var nav = document.querySelectorAll(".nav > li");
var main = document.querySelectorAll(".main > div");

for (var i = 0; i < nav.length; i++){
    nav[i].index  = i;
    nav[i].addEventListener('click',function () {
        for(var k = 0; k < nav.length; k++){
            nav[k].classList.remove('active');
            main[k].classList.remove('active');
        }
        this.classList.add('active');
        console.log(this.index);
        main[this.index].classList.add('active');
    })
}
